Multiple, Distinct Isoforms of Sucrose Synthase in Pea

• Published in: Plant physiology (Bethesda) 2001-10, Vol.127 (2), p.655-664
• Main Authors: D. H. Paul Barratt, Barber, Lorraine, Nicholas J. Kruger, Smith, Alison M., Wang, Trevor L., Martin, Cathie
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biochemical Processes and Macromolecular Structures; Biological and medical sciences; Carbon - metabolism; Cellulose; Cellulose - biosynthesis; Cloning, Molecular; Complementary DNA; DNA, Complementary; E coli; Economic plant physiology; Embryos; Enzymes; Escherichia coli; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial; Gene Expression Regulation, Developmental; Gene Expression Regulation, Plant; Genetic mutation; Glucosyltransferases - classification; Glucosyltransferases - genetics; Glucosyltransferases - pharmacokinetics; Isoenzymes - classification; Isoenzymes - genetics; Isoenzymes - pharmacokinetics; Kinetics; Metabolism; Models, Biological; Mutation; Net assimilation, photosynthesis, carbon metabolism. Photorespiration, respiration, fermentation (anoxia, hypoxia); Nutrition. Photosynthesis. Respiration. Metabolism; Organ Specificity; Peas; Photosynthesis, respiration. Anabolism, catabolism; Phylogeny; Pisum sativum; Pisum sativum - enzymology; Pisum sativum - genetics; Plant physiology and development; Plants; Plasmids; Protein isoforms; RNA; rug4 gene; Seeds - enzymology; Seeds - genetics; Starch - biosynthesis; Sucrose - metabolism; Sus1 gene; Sus2 gene; Sus3 gene; Testa
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.010297

Genes encoding three isoforms of sucrose synthase (Sus1, Sus2, and Sus3) have been cloned from pea (Pisum sativum). The genes have distinct patterns of expression in different organs of the plant, and during organ development. Studies of the isoforms expressed as recombinant proteins in Escherichia coli show that they differ in kinetic properties. Although not of great magnitude, the differences in properties are consistent with some differentiation of physiological function between the isoforms. Evidence for differentiation of function in vivo comes from the phenotypes of rug4 mutants of pea, which carry mutations in the gene encoding Sus1. One mutant line (rug4-c) lacks detectable Sus1 protein in both the soluble and membrane-associated fractions of the embryo, and Sus activity in the embryo is reduced by 95%. The starch content of the embryo is reduced by 30%, but the cellulose content is unaffected. The results imply that different isoforms of Sus may channel carbon from sucrose towards different metabolic fates within the cell.